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Why exercise won’t make you thin

Don’t touch that ‘justified’ post-workout pastry or venti Starbucks — apparently it undoes the good work of the exercise:

In what has become a defining experiment at the University of Louisiana, led by Dr Timothy Church, hundreds of overweight women were put on exercise regimes for a six-month period. Some worked out for 72 minutes each week, some for 136 minutes, and some for 194. A fourth group kept to their normal daily routine with no additional exercise.

Against all the laws of natural justice, at the end of the study, there was no significant difference in weight loss between those who had exercised – some of them for several days a week – and those who hadn’t. (Church doesn’t record whether he told the women who he’d had training for three and half hours a week, or whether he was wearing protective clothing when he did.) Some of the women even gained weight.

Church identified the problem and called it “compensation”: those who exercised cancelled out the calories they had burned by eating more, generally as a form of self-reward. The post-workout pastry to celebrate a job well done – or even a few pieces of fruit to satisfy their stimulated appetites – undid their good work. In some cases, they were less physically active in their daily life as well.

Another study, perhaps more interesting, asks if we’re confusing cause and effect. The author argues that the environmental factors we tend to obsess about in the fight against obesity – playing fields, PE time in school, extracurricular activities, parental encouragement – are actually less of a factor in determining what exercise we do than our own bodies. “An evolutionary biologist would say physical activity is the only voluntary means you have of varying or regulating your energy expenditure. In other words, what physical activity you do is not going to be left to the city council to decide. It’s going to be controlled, fundamentally, from within.”

The title of his latest research is: “Fatness leads to inactivity, but inactivity does not lead to fatness”. Wilkin is nearing the end of an 11-year study on obesity in children, which has been monitoring the health, weight and activity levels of 300 subjects since the age of five. When his team compared the more naturally active children with the less active ones, they were surprised to discover absolutely no difference in their body fat or body mass.

That’s not to say that exercise is not making the children healthy in other ways, says Wilkin, just that it’s having no palpable effect on their overall size and shape. “And that’s a fundamental issue,” he adds, “because governments, including ours, use body mass as an outcome measure.” In other words, obesity figures are not going to improve through government-sponsored programmes that focus primarily on exercise while ignoring the behemoth of a food industry that is free to push high-calorie junk to kids (and, for that matter, adults).

For one thing, Wilkin believes he has discovered another form of “compensation”, similar to Timothy Church’s discovery that we reward ourselves with food when we exercise. Looking at the question of whether it was possible to change a child’s physical activity, Wilkin’s team put accelerometers on children at schools with very different PE schedules: one which offered 1.7 hours a week, and another that offered nine hours.

“The children did 64% more PE at the second school. But when they got home they did the reverse. Those who had had the activity during the day flopped and those who hadn’t perked up, and if you added the in-school and out-of-school together you got the same. From which we concluded that physical activity is controlled by the brain, not by the environment – if you’re given a big opportunity to exercise at one time of day you’ll compensate at another.”

Wilkin argues that the environmental factors we tend to obsess about in the fight against obesity – playing fields, PE time in school, extracurricular activities, parental encouragement – are actually less of a factor in determining what exercise we do than our own bodies. “An evolutionary biologist would say physical activity is the only voluntary means you have of varying or regulating your energy expenditure. In other words, what physical activity you do is not going to be left to the city council to decide. It’s going to be controlled, fundamentally, from within.”

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(however…) “What we want to avoid is people thinking they can control their weight simply by dieting,” adds Jebb, who points out that this is the very scenario that encourages anorexia in teenage girls